Robotic heads are very popular creations -- both as parts of
larger (generally, walking)
'bots, and as separate BEAMbots in their own right.
Essentially all BEAM heads track something -- motion, light,
heat, etc.

Both 1- and 2-axis heads have been built to date. 2-axis
heads have twice as many parts as do 1-axis heads, but
otherwise are not much more complex (since they are
controlled via 2 identical circuits, one for each axis of
motion).